I am not a string player so usage of those extended techniques does not come naturally to me. I did use pizzicato briefly in the basses. You mention measures 65 - 86 - I intended those figures to be under a single legato/phrase marking but admittedly, this was a rush job so I didn't get to include all the little details in the score that I should have perhaps.
Hmm I would say the simplest and conventional way would be to use pizzicato, and yea you should have use more pizzicato to make the work more interesting.
Other than that, I agree with your comments! Just a quick tip in musescore 3 as I used to use it for composing, if you want the marking to be for example mp, but for the midi to sound mf, u could notate it down mp on the score first, then add a second dynamic marking mf directly on top of it and make it invisible. That way, it says it's mp but it's actually mf! Disclaimer though, I don't think it works the other way round, it only applies when the invisible dynamic marking is louder than the visible one as musescore takes the louder one as preference. As for such, you could put an invisible dynamic marking on the very next note as a workaround.